This is a continuation-in-part of U.S. application Ser. No. 09/907,429, filed Jul. 17, 2001now U.S. Pat No. 6,588,480, which claims priority from provisional application Ser. No. 60/219,926, filed Jul. 21, 2000 both of which are hereby incorporated herein by reference.
The present invention relates to a drum for wrapping a cord. The cord may be a lift cord, used for raising and lowering a window blind or other window covering, it may be a drive cord for driving a mechanism within a window covering, it may be a tilt cord, which tilts the slats open and closed, or it may be used for other purposes, including purposes unrelated to window blinds or shades.
Typically, a blind transport system will have a top head rail which both supports the blind and hides the mechanisms used to raise and lower or open and close the blind. Such a blind system is described in U.S. Pat. No. 6,536,503, which is hereby incorporated herein by reference. The raising and lowering usually is done by a lift cord attached to the bottom rail (or bottom slat). The tilting of the slats in the blind is typically accomplished with ladder tapes (and/or tilt cables) which run along the front and back of the stack of slats. The lift cords (in contrast to the tilt cables) may either run along the front and back of the stack of slats or they may run through slits in the middle of the slats, and they are connected to the bottom rail.
Many different drive mechanisms are known for raising and lowering blinds and for tilting the slats. A cord drive to raise or lower the blind is very handy. It does not require a source of electrical power, and the cord may be placed where it is readily accessible, avoiding any obstacles.
In prior art cord drives used for blinds, it is typical for the same cord to be used to drive the lift action and to extend through the slats and fasten to the bottom slat (or bottom rail) to lift the blind. However, it is also known to use one cord to drive the lift action (a drive cord) and another cord to lift the blind (a lift cord). Various types of drums are used for driving the lift, driving the tilt, and wrapping up the lift cords as the blind is raised and lowered. Some drums shift longitudinally as they wrap up the cord, in order to keep the cord from overwrapping onto itself, and others use other mechanisms, such as kickers, to guide the cord onto the drum while preventing overwrapping. The mechanisms that shift longitudinally are fairly complex, requiring many moving parts. The mechanisms that rely on kickers work well, but they create large thrust forces and therefore large frictional forces as the kicker pushes the cord along the drum.